Apparatus and method for fortification of black pigment based ink using black dye based ink

ABSTRACT

A method and apparatus for improving the print quality of a print job having black content. The black content is configured to be applied on a predetermined location on a print medium. In the method, the black content is fortified by applying a black dye based ink on the predetermined location and the black content is printed by applying a black pigment based ink on the predetermined location. The apparatus includes a first printhead configured to fire black dye based ink droplets on the print medium, a second printhead configured to fire black pigment based ink droplets on the print medium and a processing system configured to fortify the black content by controlling the first printhead to fire droplets on the predetermined location. The processing system is further configured to print the black content by controlling the second printhead to fire droplets on the predetermined location.

FIELD OF THE INVENTION

This invention relates generally to printers, and more particularly,although not exclusively, to inkjet printers.

BACKGROUND OF THE INVENTION

It is generally known that inkjet printers utilize black pigment basedinks to print text and line drawings. This is due to pigment based inksbeing relatively more opaque and lightfast than dye based inks. However,dye based inks are particularly suited to the production of colorimages. In this regard, conventional printers designed to print bothtext and color images may utilize a black pigment based ink and a set ofdye based inks (e.g., cyan, yellow and magenta). For example, U.S. Pat.No. 5,745,140, assigned to the HEWLETT-PACKARD COMPANY, discloses acolor inkjet printer with pigment black and dye based color inks and thedisclosure of which is hereby incorporated by reference in its entirety.

While black pigment based ink is generally regarded as being superior toblack dye based ink for text and line drawing, conventional blackpigment based ink does have a number of disadvantages. Specifically,conventional black pigment based ink has a greater capacity to clog theprinthead nozzles. In an effort to reduce the effects of decap (e.g.,clogged nozzles, pigment migration, etc.), a multitude of patents havedisclosed various manner of improvements. For example, inks withextended drying times have been developed. However, slow drying inksgenerally produce higher levels of image quality defects associated withso-called “bleed”. Bleed is a term of art used to describe excessivespreading of an ink on a print medium as well as the infiltration of onecolor into another on the print medium. In this regard, U.S. Pat. No.6,086,198, assigned to the HEWLETT-PACKARD COMPANY, discloses a set ofinks for reducing or eliminating color bleed, the disclosure of which ishereby incorporated by reference in its entirety.

Additionally, while pigment based ink is relatively more opaque than dyebased ink, to ensure highly opaque black regions, various conventionalprinting systems have been developed to “fortify” black printed areas.Some of these fortification methods have the added benefit of reducingthe drying time by utilizing an interaction between the dye based andpigment based inks. For example, it is generally known to use dye basedcyan and magenta (colored) inks as a fortification for pigmented blackink. The colored inks are deposited on the print medium and the blackink is subsequently deposited over the colored inks. The colored inksand the black ink may interact. Thus producing a more opaque black thatdries relatively faster and bleeds relatively less. However, to reducethe possibility of the colored inks being visible around the edges ofthe black region, the colored inks are not deposited around the edges ofthe black region. Due to the lack of fortification about the edges ofblack regions, color fortification of black regions may not adequatelyconceal defects associated with decap. Furthermore, hue shift defects(e.g., purple tones) are often evident in regions of colorfortification.

SUMMARY OF THE INVENTION

In one respect, the invention pertains to a method of improving theprint quality of a print job having black content. The black content hasa predetermined location on a print medium. In the method, the blackcontent is fortified by applying a black dye based ink on thepredetermined location and the black content is printed by applying ablack pigment based ink on the predetermined location.

In another respect, the invention pertains to an apparatus for improvingthe print quality of a print job having black content. The black contenthas a predetermined location on a print medium. The apparatus includes afirst printhead configured to fire black dye based ink droplets on theprint medium, a second printhead configured to fire black pigment basedink droplets on the print medium and a processing system configured tofortify the black content by controlling the first printhead to firedroplets on the predetermined location. The processing system is furtherconfigured to print the black content by controlling the secondprinthead to fire droplets on the predetermined location.

In comparison to known prior art, certain embodiments of the inventionare capable of achieving certain aspects, including some or all of thefollowing: (1) elimination of hue shift defects associated with colorfortification of black pigment based ink; (2) improving throughput viathe removal of fortification firmware; (3) reducing defects associatedwith decap and (4) improving image quality on glossy print medium. Thoseskilled in the art will appreciate these and other aspects of variousembodiments of the invention upon reading the following detaileddescription of a preferred embodiment with reference to the below-listeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic view illustrating a portion of aprinting device according to an embodiment of the invention;

FIG. 2 is a flow chart of a method, according to an embodiment of theinvention; and

FIG. 3 is a block diagram of a system, according to an embodiment of theinvention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

For simplicity and illustrative purposes, the principles of theinvention are described by referring mainly to an exemplary embodimentthereof, particularly with references to a system to fortify blackpigment based ink with black dye based ink. However, one of ordinaryskill in the art would readily recognize that the same principles areequally applicable to, and may be implemented in, a system capable ofunder laying one colorant with a second, similarly colored, coloranthaving dissimilar chemistry, and that any such variations are within thescope of the invention. While in the following description numerousspecific details are set forth in order to provide a thoroughunderstanding of an embodiment of the invention, in other instances,well known methods and structures have not been described in detail soas not to obscure the invention.

As seen in FIG. 1, there is schematically illustrated part of a printerdevice (e.g., a printer) suitable for implementation in an embodiment ofthe invention. The printer has an array of printheads 100 in asubstantially parallel row. More specifically, FIG. 1 illustrates twoprintheads 102 and 104. Each of the printheads 102 and 104 includes aplurality of printer nozzles (not shown), arranged in one or more rows,for firing ink onto a print medium 110 e.g., sheet of paper. AlthoughFIG. 1 depicts the printer as having two printheads 102 and 104, printerdevices have been known to possess any number of printheads, e.g.,three, four, or more.

Typically, the printheads 102 and 104 may be constrained to move in adirection 130 with respect to the print medium 110. In addition, theprint medium 110 may be constrained to move in a further direction 120.During a normal print operation, the printheads 102 and 104 may be movedinto a first position with respect to the print medium 110 and aplurality of ink droplets may be fired from the same plurality ofprinter nozzles contained within each of the printheads 102 and 104. Inthis manner, pixels (e.g., spots) of ink similar to pixels 106-108 maybe placed on the print medium 110. After completion of a printoperation, the printheads 102 and 104 may be moved in a direction 130 toa second position and another print operation is performed. In a likemanner, the printheads 102 and 104 may be repeatedly moved in adirection 130 across the print medium 110 and a print operation may beperformed after each such movement of the printheads 102 and 104. Whenthe printheads 102 and 104 reach an edge of the print medium 110, theprint medium may be moved a short distance in a direction 120, parallelto a main length of the print medium 110, and another print operationmay be performed. The printheads 102 and 104 may then moved in adirection 130 back across the print medium 110 and yet another printoperation may be performed. In this manner, a complete printed page maybe produced.

A more detailed description of the printer device illustrated in FIG. 1may found in commonly assigned application Ser. No. 09/502,667 filed onFeb. 11, 2000, by Xavier Bruch et al., the disclosure of which is herebyincorporated by reference in its entirety.

In the following description of FIG. 2, and for the purpose of thisdisclosure, the terms “fortify” and its variants, as used herein, may bedefined as the production of a black region with a black dye based inkand a black pigment based ink. The black dye based ink may be said tofortify the black pigment based ink. The black dye based ink may fortifya subset or essentially every pixel location within the black region.Additionally, the term “black content” refers to any type of text, lineand/or image produced with at least some black ink.

FIG. 2 is a flow chart of a method 200, according to an embodiment ofthe invention. As depicted in FIG. 2, the method 200 is initiated inresponse to receiving a print job at step 210. The print job istypically initiated by a user operating a computer or terminal on thelocal area network (“LAN”) in which a printer is located. However, it iswithin the scope of this invention that the print job may be received inany manner known to those skilled in the art. For example, the printermay be directly attached to a computer. Furthermore, it is within thescope of this invention that the printer and the print job input device(e.g., keyboard, scanner, etc.) is a single device. For example, anelectronic typewriter and/or “all in one device”, such as aprinter/copier/fax machine.

At step 220, in a manner known to those skilled in the art, the printjob may be converted into a stream of data corresponding to printerspecific commands generated in response to the print job. In general,the printer specific commands may include commands associated with mediamovement, printhead movement, nozzle firing, etc.

At step 230, it may be determined if the print medium is incompatiblewith pigment based ink. An example of a print medium that isincompatible with pigment based ink is glossy print medium because thepigment may not properly adhere and may flake off. Additionally, pigmentbased ink may produce a noticeably different sheen on glossy printmedium and thus, may be unacceptable for certain printing applications(e.g., photo imaging and the like). Furthermore other print medium(e.g., various plastics, certain fabric, etc.) may also be incompatiblewith pigment based ink. In any event, if it is determined that the printmedium is incompatible with pigment based ink, the method 200 mayproceed to step 240. If it is determined that the print medium iscompatible with pigment based ink, the method 200 may proceed to step250.

At step 240, the printer specific commands may be accessed, modified asrequired and in a process known to those skilled in the art, utilized tocontrol the movements and operations of the printer. Modifications madeto the printer specific commands may include essentially replacingcommands associated with pigment based ink with commands associated withdye based inks. Typically, conventional inkjet printers utilize“process” black to replace pigment based black ink when printing onpigment incompatible medium. The terms “process” and “composite” blackmay be defined as black color that is produced by mixing a plurality ofcolored inks (e.g., cyan, yellow and magenta) on the print medium.However, producing process black may decrease throughput. Process blackmay also be more prone to hue shift defects and thus, may not appeartruly black. The method 200 may thus improve throughput and printquality by utilizing black dye based ink to replace black pigment basedink. Additionally, the method 200 may save about ⅓ to ½ of the costassociated the ink due to the relatively low cost of black dye based inkas compared to the relatively high cost of colored inks utilized toproduce process black. Following step 240, the method 200 may proceed tostep 280.

At step 250, it may be determined whether to fortify the pigment basedink. The decision may be based on some or all of the following factors:color of content, selected print mode, type of content (e.g., text,image, etc.), size and shape of area to be fortified, etc. If it isdetermined to fortify the pigment based ink, the method 200 may proceedto step 260. If it is determined to print without fortification of thepigment based ink, the method 200 may proceed to step 270.

At step 260, the printer specific commands may be accessed, modified asrequired and in a process known to those skilled in the art, utilized tocontrol the movements and operations of the printer. Modifications madeto the printer specific commands may include essentially duplicatingsome or all of the commands associated with printing certain types ofcontent. In a preferred form, some or all of the commands associatedwith printing black content may be essentially duplicated such that bothpigment based black ink and dye based black ink may be utilized to printthe black content. In various forms, fortification may be performed suchthat black dye based ink is printed as a uniform, partial densitypattern coextensive with the black content. In other forms,fortification may be performed such that the edges, the interior or theentirety of the black content is printed with both black dye based inkand black pigment based ink.

Contrary to conventional fortification methods utilizing process black,in the method 200, it may be preferable to apply the black dye basedink, at least, on the edge of the black content. In this regard, due tothe fact that image quality defects associated with hue shift aregenerally not exhibited when fortifying black pigment based ink withblack dye based ink, fortification on the edge of the black content withblack dye based ink may reduce image quality defects associated withdecap. Following step 260, the method 200 may proceed to step 280.

At step 270, the printer specific commands may be accessed and in aprocess known to those skilled in the art, utilized to control themovements and operations of the printer to print the content withoutfortification. Following step 270, the method 200 may proceed to step280.

At step 280, the printer specific commands may be accessed to determinewhether the print job has been completed. For example, if an end of file(“EOF”) is encountered, it may be determined that the print job has beencompleted. If it is determined the print job has been completed, themethod 200 may return to the idle step to wait for another print job. Ifit is determined content remains to be printed, the method 200 mayreturn to step 220.

The method 200 may exist in a variety of forms both active and inactive.For example, they may exist as software program(s) comprised of programinstructions in source code, object code, executable code or otherformats. Any of the above may be embodied on a computer readable medium,which include storage devices and signals, in compressed or uncompressedform. Exemplary computer readable storage devices include conventionalcomputer system RAM (random access memory), ROM (read only memory),EPROM (erasable, programmable ROM), EEPROM (electrically erasable,programmable ROM), flash memory, and magnetic or optical disks or tapes.Exemplary computer readable signals, whether modulated using a carrieror not, are signals that a computer system hosting or running thecomputer program may be configured to access, including signalsdownloaded through the Internet or other networks. Concrete examples ofthe foregoing include distribution of the program(s) on a CD ROM or viaInternet download. In a sense, the Internet itself, as an abstractentity, is a computer readable medium. The same is true of computernetworks in general.

Referring to FIG. 3, there is illustrated an exemplary block diagram ofa printer 300 in accordance with the principles of the presentinvention. The following description of the block diagram illustratesone manner in which a printer 300 having a printhead 102 configured tofire droplets of black dye based ink and a printhead 104 configured tofire droplets of black pigment based ink may be operated in accordancewith the principles of the present invention. In this respect, it is tobe understood that the following description of the block diagram is butone manner of a variety of different manners in which such a printer maybe operated.

Generally speaking, the printer 300 includes the printheads 102 and 104,although additional printheads may be included. The description of theprintheads 102 and 104 in the present disclosure is for purposes ofsimplicity and is not meant as a limitation. In this regard, the printer300 may include any reasonably suitable number of printheads, e.g., two,four, six, and the like, configured to operate in the manner describedhereinbelow with respect to the printheads 102 and 104. It should beunderstood and readily apparent to those skilled in the art that thefortification technique disclosed herein may be implemented in anyreasonably suitable type of printer without departing from the scope ofthe invention.

The printheads 102 and 104 may be configured to repeatedly pass across amedium in individual, horizontal swaths or passes during a printingoperation to print a particular image (e.g., picture, text, diagrams,etc.) onto the medium. In addition, the printheads 102 and 104 may beconfigured to contain a plurality of nozzles (not shown) individuallyoperable to be implemented during each pass to apply an ink pattern ontothe medium and thus print the particular image. In this regard, theprintheads 102 and 104 may comprise conventional thermal inkjet orpiezoelectric printheads, both of which are generally known to thoseskilled in the art. In a preferred form, the fortification may beperformed in a manner such that the black dye based ink present in theprinthead 102 is fired on the print medium before the black pigmentbased ink present in the printhead 104.

The printer 300 may also include interface electronics 308. Theinterface electronics 308 may be configured to provide an interfacebetween a controller 310 of the printer 300 and the components formoving the printheads 102 and 104, e.g., a carriage, belt and pulleysystem (not shown), etc. The interface electronics 308 may include, forexample, circuits for moving the carriage, moving the medium, firingindividual resistors or piezoelectric elements in the nozzles of theprintheads 102 and 104, and the like.

The controller 310 may be configured to provide control logic for theprinter 300, which provides the functionality for the printer. In thisrespect, the controller 310 may possess a microprocessor, amicro-controller, an application specific integrated circuit, and thelike. The controller 310 may be interfaced with a memory 312 configuredto provide storage of a computer software that provides thefunctionality of the printer 300 and may be executed by the controller.The memory 312 may also be configured to provide a temporary storagearea for data/file received by the printer 300 from a host device 314,such as a computer, server, workstation, and the like. The memory 312may be implemented as a combination of volatile and non-volatile memory,such as dynamic random access memory (“RAM”), EEPROM, flash memory, andthe like. It is also within the purview of the present invention thatthe memory 312 may be included in the host device 314.

The controller 310 may further be interfaced with an I/O interface 316configured to provide a communication channel between a host device 314and the printer 300. The I/O interface 316 may conform to protocols suchas RS-232, parallel, small computer system interface, universal serialbus, etc. In addition, the controller 310 may be interfaced with a printmedium detector 302.

The print medium detector 302 may be configured to determine the printmedium type. For example, such factors as the thickness, height, widthand reflective properties of the print medium and the print mediumsource may be sensed and utilized to determine the print medium type.Additionally, various print mediums may include indicators such asnotches, bar codes and the like and the print medium detector 302 may beconfigured to sense the indicators.

Although the host device 314 is depicted as distinct from the printer300, it is widely known that the functionality of the host device 314may be subsumed within the printer 300. For example, an electronictypewriter or a printer/scanner/fax/copier machine may incorporate someor all of the functionality of the host device 314 within the printer300. The host device 314 may be configured for two way communicationwith the printer 300. In a preferred form, the host device 314 may beconfigured to forward print jobs to the printer 300. Additionally, thehost device 314 may be operable as a user interface for the printer 300.In this regard, the host device may be configured to provide thecapability to select a printmode, print medium type, etc. Furthermore,although not depicted in FIG. 3, the printer 300 may include a userinterface.

What has been described and illustrated herein is a preferred embodimentof the invention along with some of its variations. The terms,descriptions and figures used herein are set forth by way ofillustration only and are not meant as limitations. Those skilled in theart will recognize that many variations are possible within the spiritand scope of the invention, which is intended to be defined by thefollowing claims—and their equivalents—in which all terms are meant intheir broadest reasonable sense unless otherwise indicated.

What is claimed is:
 1. An apparatus for improving the print quality of a print job having black content, the black content having a predetermined location on a print medium, the apparatus comprising: a first printhead configured to fire black dye based ink droplets on the print medium; a second printhead configured to fire black pigment based ink droplets on the print medium; and a processing system configured to fortify the black content by controlling the first printhead to fire droplets on the predetermined location, the processing system being further configured to print the black content by controlling the second printhead to fire droplets on the predetermined location; wherein the processing system is further configured to determine whether the print medium is incompatible with the black pigment based ink, control the first printhead to fire droplets on the predetermined location in an essentially uniform, partial density pattern and/or in an essentially complete coverage in response to the print medium being incompatible with the black pigment based ink, and control the second printhead to omit the firing of droplets on the predetermined location in response to the print medium being incompatible with the black pigment based ink.
 2. The apparatus according to claim 1, further comprising: a user interface configured to receive a selected print mode, the user interface being configured to communicate with the processing system, wherein the processing system is further configured to determine whether the print medium is incompatible with the black pigment based ink based on the selected print mode.
 3. The apparatus according to claim 1, further comprising: a media detector configured to detect a print medium type, the media detector being configured to determine whether the print medium is incompatible with the black pigment based ink based on the print medium type. 